In January 2010, we deployed an advanced laser version of the Dust Logger in the main 3,226 meter borehole at Dome C (EDC99). An overview of the logging data is shown in Figure 1.

We made three logs using two slightly different logging probes: one probe was equipped with a 30 mW laser and the other with a 60 mW laser, and the photon counting systems on the two probes differed in response to an overflow condition. In the bubbly ice above 1200 meters depth, the detectors were typically in overflow. The data have been processed with several corrections applied. The laser brightness was found to have a substantial temperature dependence, which has been suppressed. Small logging depth errors (between about 1 to 5 m) have been suppressed using polynomial fits (4th-order for Logs 2 and 3, 1st-order for Log 1) to known core feature depths (Fig. 2).

We are compiling a list of optical anomalies that suggest the presence of a thin opaque fallout layer, typically from a volcanic eruption. We assign each anomaly a grade of ++, + or -: